This invention relates to an improvement in mortar composition suitable for masonry. Mortar, in ancient times, could be any kind of cementitous material used to bond building components together. Mud, clays, naturally occurring cement, etc. were used either alone or in a mixture. Mortar, today, suitable for unit masonry in the building trade must pass ASTM standards. In particular, ASTM standard C 270-68 is followed. While mortar is not defined by one specific composition in the industry it is generally recognized that masonry mortar consists of Portland cements, hydrated lime, and aggregates or masonry cement and aggregates which are mixed with water. The resultant mortar must have a specified water retention, i.e., greater than 70% and a compressive strength of 500 psi and 900 psi after 7 days and 28 days respectively. The cement, hydrated lime and aggregates must, in turn, each meet criteria which are defined by ASTM standards.
While it has long been recognized that hydrated lime is preferred in mortar mixtures containing Portland cement it has also been long known that the hydrated lime detracts substantially from the strength of the mortar.
Therefore, an object of the present invention is to produce a mortar containing Portland cement which does not contain hydrated lime and is able to pass the ASTM C 270-68 specification for mortar.
It is a further object of the invention to produce a mortar which upon curing has superior compressive strength, negligible expansion or contraction, and no distortion, cracking, checking, or pitting.
By the present invention it is possible to produce a mortar suitable for unit masonry which does not contain hydrated lime. This mortar passes all of the ASTM standards and, moreover, has superior workability, plasticity, and water retention. The present invention substitutes a fuller's earth type clay which has a plasticity greater than 700 and which is a calcium magnesium aluminum silicate. Preferably, the calcium magnesium aluminum silicate is a naturally occurring mineral found in Central Florida and known by the term Emathlite.
The ASTM C270-68 specification for mortar discusses various suitable cementitious materials. It should be noted that the ASTM C270-68 specification also provides standards for other types of cement designated Portland Pozzolan cement. Pozzolan is a broad descriptive term for any material which can combine with calcium oxide in the presence of water. While fuller's earth clay will fit this broad definition it is to be noted that Pozzolan cements are made by the inter-grinding of the Pozzolanic material and the Portland cement clinker. Commercially, the typical Pozzolan cement is one in which the Pozzolanic material is fly ash.
The present invention embodies the use of Portland cement combined with Emathlite, a calcium magnesium aluminum silicate, as a substitute for hydrated lime, to form a masonry cement as specified in ASTM C 91. The resultant masonry cement will meet all requirements for masonry mortar as specified in ASTM C 270-68.
The ASTM C 270-68 specification provides that the mortar is mixed to an initial flow of 100 to 115 and shall have a flow after suction of not less than 70%. The compressive strength, properly measured, shall be 500 psi after 7 days and 900 psi after 28 days.
In regard to the other terms used in the ASTM C-270-68 specification, the term hydrated lime or lime is intended to indicate material which satisfy the standard specifications for hydrated lime found in ASTM designation C 207. The lime must have a plasticity value over 200 and a water retention not less than 75%. In each instance, the term Portland cement is intended to indicate a Portland cement satisfying the specification for Portland cement found in ASTM designation C 150 and Portland blast-furnace slag cement as found in ASTM designation C 595. In each instance, the term aggregate is intended to indicate a convenient mixture of natural sand, crushed stone or gravel which is clean, chemically inert, and substantially free of organic matter. Size limitations may be placed upon the individual particles making up the aggregate, depending upon the specifications for the mortar to be used on a particular project.
By plasticity is meant that the mortar or cement can be molded, altered or otherwise deformed without rupturing or losing cohesive structure.
By water retention is meant a resistance to suction from the dry surface to which a masonry mortar is applied. All mortar when used for bonding masonry units, plaster or stucco is subjected to a suction from the dry surfaces to which it is applied. If a mortar has insufficient water retention, such a suction could rapidly remove the water from the applied mortar. Too rapid a loss of water results in the hydration period of the cements not being completed thus reducing the strength of resulting structure. Additionally, workability time is reduced thus preventing proper placement of masonry units. The too rapid loss of water results in a loss of suction which in turn results in poor bonding and cracking.
If a mortar is made from materials which provide for sufficient water retention, the suction from the dry surfaces to which it is applied will not remove the water from the mortar to any appreciable extent. In this way sufficient time is provided for proper placement of masonry units and subsequent hydration of the cements to achieve maximum strength.
Calcium magnesium aluminum silicate is a fuller's earth type clay well known for its sorptive properties. It includes highly porous montmorillonites, attapulgites, sepiolites, palygorskites, and opalites to define its geological origin. The fuller's earth is highly absorbant and when used in the present invention must form a mortar which has a water retention of greater than 70%. Additionally the fuller's earth must have a plasticity greater than 700.
These clays and clay mixtures typically contain by weight 30-70% silicon dioxide, 3-20% aluminum oxide, 3-9% calcium oxide, 1-8% magnesium oxide and 1-20% of other oxides such as iron oxides, sodium, potassium and lithium oxide, titanium oxide, sulfur oxide and 2-15% water. The physical properties of the clay, particularly, high water retention and plasticity are critical parameters which make it possible to substitute the calcium magnesium aluminum silicate for hydrated lime. The exact chemical analysis is of lesser significance and mixtures of fuller earth type clays can be made which have the desired water retention and plasticity. The chemical analysis of mixed fuller's earth clays in the present invention generally is by weight percent 50-70% silicon dioxide, 7-16% aluminum oxide, 3-9% calcium oxide, 1-7% magnesium oxide, other oxides 1-10% and water 1-10%.
A preferred fuller's earth type clay is one known as Emathlite. The chemical composition for Emathlite is is shown in Table I. Emathlite is commercially available from Mid-Florida Mining Company.
TABLE I ______________________________________ Chemical Analysis Generally Typically ______________________________________ Silicon Dioxide 60-70 66.8 Aluminum Oxide 9-15 11.5 Calcium Oxide 3-9 6.1 Magnesium Oxide 2-5 3.0 Iron Oxide 1-6 2.9 Sulfur Oxide .03-2 .1 Potassium Oxide 1-4 1.3 Titanium Dioxide 0.1-2 0.3 Sodium Oxide 0.1-2 0.2 Ignition loss at 1220.degree. C 2-9% 5.8 ______________________________________
In many ways Emathlite is an unusual material even among clays and fuller's earth materials. The Emathlite has a very high water retention, commonly 75 to 95%. Even more remarkable, the Emathlite can have plasticity value of more than 900. These properties are not associated with Pozzolanic materials in general and particularly contrast with the common construction Pozzolanic material, fly ash, which typically has a water retention of about 50% and a plasticity value of about 110.
The typical physical properties for Emathlite are summarized in Table II.
TABLE II ______________________________________ Typical Physical Properties pH 4.4-4.9 Specific Gravity 2.40 Free Moisture, % 4-6 Plasticity 700-950 Surface Area, m.sup.2 /g 700 Bulk Density, lbs./ft..sup.3 32-38 ______________________________________